John Curl's Blowtorch preamplifier part II

Status
Not open for further replies.
Jump to Latest
#33,881
Interesting! A sharp filter causes the appearance of ringing on a sharp transient, not by adding anything but by removing the higher frequencies which would otherwise cancel the appearance of ringing. So is it the phase shifts below the stopband whch were heard, or the absence of expected components above the stopband which were then misinterpreted by the ear/brain as the presence of transients?
 
#33,883
RNMarsh said:
Regarding roll-off frequencies ---> group-delay is still important to keep under a certain threshold. Dean Jensen (Jensen Transformer founder and designer) made his fame by winding his transformers for low group-delay distortion (esp. at low end).... little known at the time. But, bares repeating from time to time. especially when talking about filters. CD and the filters used are not always minimum group-delay and can/do exceed audible thresholds. It is also one to test for as a complete end-to-end system. Thx-RNMarsh
Click to expand...

And yet, when a zip cord is used between a low impedance source and a wildly varying low impedance load, the group delay caused by the transmission line effects are ignored.😕

Do you have any idea what level of delay Dean found and corrected for?
jn
 
#33,884
There is a lot to explore, about this bandwidth limitation question. There can be some side effects depending of the enclosures used for listening comparisons, by example. If they are not time aligned, it is possible a low pass filter add some phase shift with correct (or worsen) the group delay in this particular circumstance ?
 
#33,885
jan.didden said:
Of four participants, one stepped out because he admitted not hearing any difference. The remaining three, yours truly among them, all identified correctly the two different situations but inverted: we thought that the situation with the filter switched in sounded the best! We also had similar descriptions of that 'best' situation: brighter, more attack, more transients. As I said, humbling.
Click to expand...

I would rather say understandable - you have used a poor audio system for your test. 95% or maybe even more audio systems are poor, including so-called highend.
 
#33,886
vacuphile said:
Nobody has ever been able to hear ultrasonic, sort of definitional.
Click to expand...

Ultrasound - Wikipedia, the free encyclopedia

Humans

The upper frequency limit in humans (approximately 20 kHz) is due to limitations of the middle ear, which acts as a low-pass filter. Ultrasonic hearing can occur if ultrasound is fed directly into the skull bone and reaches the cochlea through bone conduction without passing through the middle ear.[3]

3. Corso, J. F. (1963). "Bone-conduction thresholds for sonic and ultrasonic frequencies". Journal of the Acoustical Society of America 35 (11): 1738–1743. Bibcode 1963ASAJ...35.1738C. doi:10.1121/1.1918804.
 
#33,887
PMA said:
after new listening tests of the buffered AD797 I find this opamp very, or I would say extremely transparent, with great resolution of highs and details, and tight solid bass. In the past I have probably not implemented it well.
Click to expand...

I would like to return to this post. After a week of listening tests, I would like to emphasize that the preamp based on AD797 with buffered output sounds great. It is extremely transparent with fantastic resolution and in the same time it is not aggressive. I mostly listen to classical philharmonic orchestra music when evaluating audio component. DGG Beethoven symphonies sets conducted by Harnoncourt and Gardiner are great through this opamp. No muffling, no blending, no rounding and also no aggressiveness. Hats off.
 
#33,889
Esperado said:
"But the fact that the listeners preferred full-range sound, if undistorted, had now been proved. "

OMHO, i prefer my speakers without tweeters (horn up to 16KHz, time aligned) but i prefer my electronic as fast as possible, and, as i said, a bandwidth up to 200Khz for my amp, and no brickwall for my CD. Hard to explain.
Click to expand...

Perhaps the physical processes responsible for the roll-off at the speaker end produce different types of distortions/alterations than the high freq distortion produced by the the various electronics.
 
Last edited:
#33,890
I just found this nifty PowerPoint presentation that goes over some of the basics:

11.1 Fundamental Concepts
11.2 High-Frequency Models of Transistors
11.3 Analysis Procedure
11.4 Frequency Response of CE and CS Stages
11.5 Frequency Response of CB and CG Stages
11.6 Frequency Response of Followers
11.7 Frequency Response of Cascode Stage
11.8 Frequency Response of Differential Pairs
11.9 Additional Examples

www.ee.ucla.edu/~brweb/teaching/ch11_new.ppt


Lots of good tidbits from an electronics course:

Index of /~brweb/teaching
 
#33,891
"I would like to return to this post. After a week of listening tests, I would like to emphasize that the preamp based on AD797 with buffered output sounds great. It is extremely transparent with fantastic resolution and in the same time it is not aggressive. I mostly listen to classical philharmonic orchestra music when evaluating audio component. DGG Beethoven symphonies sets conducted by Harnoncourt and Gardiner are great through this opamp. No muffling, no blending, no rounding and also no aggressiveness. Hats off."

Why the re-conversion to integrated opamps again PMA? People argued at length on this thread some time ago about the glories of discrete . . .
 
#33,895
Back to Slot's book 'Audio Quality' I am having trouble with my scanner.
However, on p. 52 "The effect of the response sounding brighter or shriller than when the characteristic is straight [flat frequency response] starts when the roll-off is more than 6dB/octave."
 
#33,896
RNMarsh said:
Regarding roll-off frequencies ---> group-delay is still important to keep under a certain threshold. Dean Jensen (Jensen Transformer founder and designer) made his fame by winding his transformers for low group-delay distortion (esp. at low end).... little known at the time.
Click to expand...

Actually the transformers that Deane sold under the Jensen brand were transformers designed and built by Ed Reichenbach, formerly of Altec, then with his own company, Reichenbach Engineering. Jensen was originally billed as "Jensen Transformers by Reichenbach Engineering." Deane later split from Ed, taking the engineering with him and having them wound by another company.

And it wasn't at the low end that Deane was focusing on but rather the high end, where the transformer's parasitics combine to create a resonant circuit.

Finally, the transformers are made to have more or less a 2 pole low pass Bessel function (to give the best group delay) by way of external RC networks.

Edit: Here's a photo of Ed Reichenback and his wife, Betty, wearing their "Jensen Transformers by Reichenbach Engineering" satin jackets:

An externally hosted image should be here but it was not working when we last tested it.



se
 
Last edited:
#33,897
john curl said:
'BUFFERED OUTPUT' PMA, This is not how it is normally used. Please show me the buffer, if you will? Did you compare it with an AD825 with the SAME BUFFER?
Click to expand...

No, I will not.

But output buffering, though different from mine, is shown in the AD797 datasheet, and was shown here few weeks ago. Datasheet image attached. Once again, my buffering scheme is different.

AD825 is not that transparent and does not have such good resolution - probably for the reason it is very noisy. But AD825 sounds "nice" (= equalizing).
 

Attachments

  • AD797_buf.PNG
    AD797_buf.PNG
    26.8 KB · Views: 233
#33,899
PMA said:
I would rather say understandable - you have used a poor audio system for your test. 95% or maybe even more audio systems are poor, including so-called highend.
Click to expand...

Pavel,

I am very much in awe for your uncanny capability to conclude which systems people have in their homes just by reading these posts - even more by your very astute knowledge that 95% of these systems are poor. That must have cost quite some time to listen to all of them and count them! 😀

jan
 
Status
Not open for further replies.
Top Bottom